1. Field of the Invention
The present invention relates generally to catheter systems for imaging and treatment of stenoses within a patient's vascular system and more particularly to a catheter system in which a balloon angioplasty device can be delivered along with an imaging or interventional work element to a desired region within a blood vessel.
2. Description of the Background Art
Arteriosclerosis, also known as atherosclerosis, is a common human ailment arising from the deposition of fatty-like substances, referred to as atheroma or plaque, on the walls of blood vessels. Such deposits occur both in peripheral blood vessels that feed limbs of the body and coronary blood vessels that feed the heart. Localized accumulation of deposits within regions of the blood vessels may result in stenosis, or narrowing of the vascular channel. When this occurs, blood flow is restricted and the person's health is at serious risk.
Numerous approaches for reducing and removing such vascular deposits have been proposed, including balloon angioplasty, in which a balloon-tipped catheter is used to dilate a stenosed region within the blood vessel; atherectomy, in which a blade or other cutting element is used to sever and remove the stenotic material; laser angioplasty, in which laser energy is used to ablate at least a portion of the stenotic material; and the like.
In order to apply such intervention techniques more effectively, a variety of vascular imaging devices and methods may be employed. Of particular interest to the present invention, imaging catheters having ultrasonic transducers at their distal ends have been employed to produce images of the stenotic region from within the blood vessel.
A number of specific designs for ultrasonic imaging catheters have been described. An early design is illustrated in U.S. Pat. No. 4,794,931, where the mechanical components of the imaging system are located within a housing at the distal end of the catheter. The housing includes a fixed guidewire, which is used to position the catheter within the vascular system, at its distal tip. While the use of such fixed-guidewire designs can provide excellent image quality, under some circumstances it is desirable to use an "over-the-wire" design where the catheter may be introduced over a separate (movable) guidewire. The use of a movable guidewire offers certain advantages, including improved steering capability through narrow regions and easier catheter exchange, e.g., substitution of an interventional catheter for the imaging catheter.
Exchanging the imaging catheter for an interventional or other catheter within a patient's vascular system is time consuming and may be injurious to the patient. It is desirable therefore to combine imaging and interventional capabilities in a single catheter system. A design for an ultrasonic imaging catheter having a balloon angioplasty device is described in U.S. Pat. No. 5,117,831. One depicted embodiment uses a fixed guidewire and is thus subject to the disadvantages noted above. Another embodiment has a guidewire movable through the ultrasonic imaging transducer and its associated drive shaft. This requires that the transducer and the drive shaft be made hollow and increased in diameter in order to accommodate the guidewire therein. Additionally, the transducer is fixed at the end of the drive shaft and not movable along the length of the catheter.
To be able to cross very narrow lesions, the diameter of the catheter should be as small as possible at its distal end. Furthermore, the need to move the catheter body within the patient should be minimized. The blood vessel interior is delicate, may be weakened by disease, and is therefore susceptible to injury from movement of the catheter body within it.
For the reasons stated above, it would be advantageous to provide a catheter capable of delivering a balloon angioplasty system in combination with an imaging or interventional work element to a region of interest within the vascular system. Such delivery should be accomplished with a minimum repositioning of the catheter body within the blood vessel. Additionally, the catheter should be as narrow as possible at its distal end to allow for entry into and through narrow and tortuous regions of the patient's vascular system.